1. Field of the Invention
The present invention relates to multilayer ceramic capacitors, and more particularly, to borosilicate glass compositions for a sintering agent, dielectric compositions containing the borosilicate glass compositions and a multilayer ceramic capacitor using the dielectric compositions that allow low-temperature sintering and improve hot insulation resistance.
2. Description of the Related Art
Recently, with rapid advancements in miniaturization, lightweight and multifunctionality of electrical and electronic devices, multilayer ceramic capacitors (MLCCs), used in these electric and electronic products, have been reduced in weight and increased in capacitance. Dielectric layers, used in multilayer ceramic capacitors, are also continually being reduced in thickness, and the number of dielectric layers being laminated is growing increasingly large.
Important factors, which need to be taken into account when developing ultra high capacitance multilayer ceramic capacitors, include the realization of exceptionally high capacitance and ensuring a high level of reliability. In general, the reliability of multilayer ceramic capacitors is determined according to the results of evaluating hot insulation resistance and humid insulation resistance. Hot insulation resistance is generally determined by material factors, such as the degradation characteristics of dielectrics or internal electrode materials, and the microstructural defects in them. Humid insulation resistance is determined by processing factors, such as interlayer defects and micro-cracks in marginal area or inside the external electrodes, which are caused by process failures. In particular, when hundreds of ultra-thin dielectric layers are stacked and fired for preparing the ultra high capacitance MLCCs with an X5R thermal property, insulation resistance rapidly decreases as a DC voltage is applied at a usable temperature of 85° C. or less. Therefore, in order to develop ultra high capacitance MLCCs, it is necessary to ensure that dielectric materials have the properties of high permittivity and enhanced hot insulation resistance at the same time.
Furthermore, in order to manufacture ceramic capacitors having ultra-thin dielectric layers, dielectric compositions that can be sintered at low temperatures need to be used. When a sintering process is performed at high temperatures in order to manufacture multilayer ceramic capacitors, sintering shrinkage mismatch occurs between dielectric layers and internal electrodes, and an agglomeration of the internal electrodes is worsened. As a result, the capacitance of the ceramic capacitors is reduced, and the short ratio increases.
However, sintering agents in general use have an optimum sintering temperature ranging from 1500° C. to 1200° C. and thus are not appropriate for use when manufacturing a multilayer ceramic capacitor having ultra-thin dielectric layers.
Therefore, in order to manufacture ultra high capacitance MLCCs with high reliability that include ultra-thin dielectric layers, dielectric compositions that can be sintered at low temperatures and have enhanced hot insulation resistance are required.